Electron beam devices, in particular a scanning electron microscope (also referred to as SEM below) and/or a transmission electron microscope (also referred to as TEM below), are used to examine objects (also referred to as samples) in order to obtain knowledge in respect of the properties and behavior of the objects under certain conditions.
In an SEM, an electron beam (also referred to as primary electron beam below) is generated by means of a beam generator and focused on an object to be examined, by means of a beam guiding system. An objective lens is used for focusing purposes. The primary electron beam is guided over a surface of the object to be examined by means of a deflection device. This is also referred to as scanning. The area scanned by the primary electron beam is also referred to as scanning region. Here, the electrons of the primary electron beam interact with the object to be examined. Interaction particles and/or interaction radiation result as a consequence of the interaction. By way of example, the interaction particles are electrons. In particular, electrons are emitted by the object—the so-called secondary electrons—and electrons of the primary electron beam are scattered back—the so-called backscattered electrons. The interaction particles form the so-called secondary particle beam and are detected by at least one particle detector. The particle detector generates detection signals which are used to generate an image of the object. An image of the object to be examined is thus obtained. By way of example, the interaction radiation is X-ray radiation or cathodoluminescence light. At least one radiation detector is used to detect the interaction radiation.
In the case of a TEM, a primary electron beam is likewise generated by means of a beam generator and directed onto an object to be examined, by means of a beam guiding system. The primary electron beam passes through the object to be examined. When the primary electron beam passes through the object to be examined, the electrons of the primary electron beam interact with the material of the object to be examined. The electrons passing through the object to be examined are imaged onto a luminescent screen or onto a detector—for example in the form of a camera—by a system comprising an objective. By way of example, the aforementioned system additionally also comprises a projection lens. Here, imaging may also take place in the scanning mode of a TEM. Such a TEM is referred to as STEM. Additionally, provision may be made for detecting electrons scattered back at the object to be examined and/or secondary electrons emitted by the object to be examined, by means of at least one further detector in order to image the object to be examined.
Combining the functions of an STEM and an SEM in a single particle beam device is known. It is therefore possible to carry out examinations of objects with an SEM function and/or with an STEM function using this particle beam device.
Moreover, a particle beam device in the form of an ion beam column is known. Ions used for processing an object are generated using an ion beam generator arranged in the ion beam column. By way of example, material of the object is ablated or material is applied onto the object during the processing. The ions are additionally or alternatively used for imaging.
Furthermore, the prior art has disclosed the practice of analyzing and/or processing an object in a particle beam device using, on the one hand, electrons and, on the other hand, ions. By way of example, an electron beam column having the function of an SEM is arranged at the particle beam device. Additionally, an ion beam column, which has been explained further above, is arranged at the particle beam device. The electron beam column with the SEM function serves, in particular, for examining further the processed or unprocessed object, but also for processing the object.
When generating an image of the object, the user of an electron beam device is always intent on obtaining the ideal image quality of an image of the object which is required for examining an object. Expressed differently, a user always wishes to generate an image of the object with such a high image quality that the user is able to analyze the object to be examined well on account of the image and the image information contained therein.
As mentioned above, it is also possible to detect interaction radiation, for example cathodoluminescence light and X-ray radiation. When detecting interaction radiation, a user of an electron beam device may, above all, be intent on obtaining the quality of the representation of the detection signals of a radiation detector based on the detected interaction radiation which is required for examining an object. By way of example, if X-ray radiation is detected by the radiation detector, the quality of the representation is determined e.g. by a good detection signal of the radiation detector.
The quality of an image and of the representation of the detection signals based on the detected interaction radiation depend on vibrations, in particular generated by pumps used to generate a vacuum within the electron beam device and by valves connecting chambers of the electron beam device to the pumps. A known electron beam device comprises a vacuum chamber. The vacuum chamber may comprise a particle generator for generating an electron beam having electrons and/or may comprise the object to be imaged, analyzed and/or processed. A turbomolecular pump is in fluid connection with the vacuum chamber. Moreover, the turbomolecular pump is in fluid connection with a vacuum reservoir. A first valve is arranged between the turbomolecular pump and the vacuum reservoir. The fluid connection between the turbomolecular pump and the vacuum reservoir may be connected or disconnected using the first valve. The vacuum reservoir is in fluid connection with a roughing pump. A second valve is arranged between the vacuum reservoir and the roughing pump. The fluid connection between the vacuum reservoir and the roughing pump may be connected or disconnected using the second valve.
The roughing pump is used for establishing a vacuum with a low vacuum reservoir pressure existing in the vacuum reservoir. The low vacuum reservoir pressure may be equal to or higher than 0.1 Pa. When the vacuum reservoir pressure reaches a low threshold, the roughing pump is disconnected from the vacuum reservoir. The low threshold may be 0.2 Pa, example. In other words, the second valve is closed such that the fluid connection between the vacuum reservoir and the roughing pump is disrupted. Moreover, the vacuum reservoir is connected to the vacuum chamber. In other words, the fluid connection between the vacuum reservoir and the vacuum chamber is established by opening the first valve. When the fluid connection between the vacuum chamber and the vacuum reservoir is established, the vacuum reservoir pressure existing in the vacuum reservoir increases. When the vacuum reservoir pressure reaches a given threshold of the vacuum reservoir pressure, the first valve is closed such that the fluid connection between the vacuum chamber and the vacuum reservoir is disrupted. Moreover, the roughing pump is connected again to the vacuum reservoir by opening the second valve. The vacuum reservoir is evacuated using the roughing pump. The above-mentioned circle may be repeated as much as needed and while the electron beam device is in operation.
The opening and closing of the first valve and the second valve may cause disturbances to the electron beam device. These disturbances may be vibrations. Moreover, the vibrations may be caused by evacuating the vacuum reservoir. If an object is imaged during the occurrence of such disturbances, the obtained image of the object may be of insufficient quality and, therefore, imaging of the object has to be repeated for obtaining a high-quality image of the object. The aforementioned may also be a problem when large objects are automatically imaged and when a user of the electron beam device is not present all the time during imaging. An image of a large object may take up to hundreds of hours. If several of the disturbances occur at different times during the whole process of imaging the large object, several of the obtained images may be of insufficient quality. A user has to manually pick out those images not being of sufficient quality and recapture those images. Moreover, the disturbances may cause damage during an operation using a micromanipulator used for arranging the object within an object chamber of the electron beam device. The micromanipulator may collide with the object or with a part of the electron beam device when those disturbances occur. This may destroy the object and damage the micromanipulator.
Accordingly, it is desirable to provide a method for imaging not impaired by the aforementioned disturbances. As one possible solution it is known to leave the first valve and the second valve open such that there always exists a fluid connection between the vacuum chamber, the vacuum reservoir and the roughing pump. However, this may also have a negative influence on the quality of the obtained images since a roughing pump having a constant fluid connection would keep running, which may lead to a decrease of the signal-to-noise ratio with respect to the obtained images.
Therefore, it is an object of the system described herein to specify a method for operating a pressure system, in particular a vacuum system, of a device for imaging, analyzing and/or processing an object and a device for carrying out this method which provide for sufficient quality of an image of the object although disturbances caused by valves might occur.